PRINCIPLES OF OPERATION
REV.-A
Chopper OFF Time (t1-t2)
(6)
(7)
(8)
(9)
When Q1 goes OFF, reverse potential is generated in the motor coil, causing the coil current route to
switch from I
ON
to I
OFF
.
I
OFF
flow then causes current flow in R6 to change direction. COMP1 feedback voltage V
RS
(V-) thereby
drops below
V
REF
,
and COMP1 again inverts.
COMP1 output stages are formed by an open collector circuit. As a result of the inversion in step (7),
COMP1 output goes HIGH, so that
T
D
voltage
V
TD
gradually rises, in line with the time constant deter-
mined by resistance R10 and capacitance C46.
The MOSFET gate voltage is maintained at OFF until the value of the T
D
voltage reaches the COMP2
reference voltage of 2 V.
The period above, during which
V
TD
is rising from 0 V to 2 V, is equivalent to
T
OFF
.
Chopper ON Time (t2-t3)
(10) When T
D
voltage V
TD
reaches the COMP2 reference value (2 V), COMP2 inverts, and Q1 goes on.
(11) When Q1 goes on, the current flow switches from
I
OFF
to
I
ON
.
(12) On the basis of the time content of motor coil A,
I
ON
,
after a certain delay, gradually rises in response
to power source voltage Vcc.
(13) As I
ON
increases, R6 potential V
RS
also increases. Until the value of
V
RS
reaches that of V
REF
, Q1 re-
mains on, supplying current I
ON
from the power source to the motor.
The period in which
V
RS
advances toward
V
TD
is equivalent to
T
ON
.
2-46
LQ-510
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